Design Considerations for Borehole Thermal Energy Storage (BTES): A Review with Emphasis on Convective Heat Transfer

Table 3

Thermal velocities and equivalent thermal travel distances for a range of Darcy fluxes (and equivalent hydraulic conductivities, given a groundwater head gradient of 0.01). For reference, hydraulic conductivities of 10^-2 to 10^-4 m s^-1 are typical of sands, 10^-5 to 10^-7 m s^-1 are typical of rather fine sands, silts, and loams. A bulk volumetric heat capacity of 2.4 MJ m^-3 K^-1 is assumed for the aquifer.

Hydraulic conductivity with head	Darcy flux	Hydraulic velocity if	Hydraulic velocity if	Thermal velocity	Heat travel distance in 6 months	Heat travel distance in 1 year
m s^-1	m d^-1	m d^-1	m d^-1	m d^-1	m	m
	0.0001	0.01	0.0005	0.0002	0.0	0.1
	0.0005	0.05	0.0025	0.0009	0.2	0.3
	0.001	0.1	0.005	0.0017	0.3	0.6
	0.005	0.5	0.025	0.0087	1.6	3.2
	0.01	1	0.05	0.0175	3.2	6.4
	0.05	5	0.25	0.0873	15.9	31.9
	0.1	10	0.5	0.17	31.9	63.7
	0.5	50	2.5	0.87	159	319
	1	100	5	1.75	319	637
	5	500	25	8.73	1593	3186
	10	1000	50	17.5	3186	6372